[Lowfer] Has anybody tried...

[Lyle Koehler]

The specification sheet for the AD9850 DDS chip says that:

"the output frequency can be digitally changed (asynchronously) at a rate of
up to 23 million new frequencies per second. The device also provides five
bits of digitally controlled phase modulation, which enables phase shifting
of its output in increments of 180�, 90�, 45�, 22.5�, 11.25� and any
combination thereof. "

I guess the limitation would be in what device you're using to send the
commands to the DDS chip.

For LowFER or MedFER operations, where your signal is so weak that the "key
clicks" are not likely to be objectionable, an exclusive-OR gate can be used
as a PSK modulator. My article on "WOLF for beginners" at
http://www.computerpro.com/~lyle/wolf/wolf4beginners.htm includes circuits
for PSK modulation of an RF carrier by an on-off keyed audio signal. Stewart
Nelson's WOLF software can generate an on-off keyed "wolfx.wav" file, and
the Digimode Terminal in DL4YHF's Spectrum Lab software also provides an
option for generating on-off keyed audio. I'm using Spectrum Lab at the
moment to send "PSK128", although I'm using a new, supposedly improved audio
detector circuit for the higher speed stuff. Will post a schematic to my web
page soon.

Lyle